1. Technical Field
This invention relates generally to a method and apparatus for separating valuable material from unwanted material in a mixture, such tailings of a flotation process.
2. Description of Related Art
In many industrial processes, flotation is used to separate valuable or desired material from unwanted material. By way of example, in this process a mixture of water, valuable material, unwanted material, chemicals and air is placed into a flotation cell. The chemicals are used to make the desired material hydrophobic and the air is used to carry the material to the surface of the flotation cell. When the hydrophobic material and the air bubbles collide they become attached to each other. The bubble rises to the surface carrying the desired material with it.
The performance of the flotation cell is dependent on the bubble surface area flux in the collection zone of the cell. The bubble surface area flux is dependent on the size of the bubbles and the air injection rate. Controlling the bubble surface area flux has traditionally been very difficult. This is a multivariable control problem and there are no dependable real time feedback mechanisms to use for control.
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. The process has been adapted and applied to a wide variety of materials to be separated, and additional collector agents, including surfactants and synthetic compounds have been adopted for various applications. The flotation process is used for the separation of a large range of sulfides, carbonates and oxides prior to further refinement. Phosphates and coal are also upgraded (purified) by flotation technology. Froth flotation commences by comminution (that is, crushing and grinding), which is used to increase the surface area of the ore for subsequent processing. The ore include the desired minerals and other unwanted materials, know a gangue. The process of grinding the ore into a fine power is known as liberation. The fine powder ore is then mixed with water to form pulp slurry. The desired mineral is rendered hydrophobic by the addition of a surfactant or collector chemical. The particular chemical depends on which mineral is being refined. This slurry (more properly called the pulp) of hydrophobic mineral particles and hydrophilic gangue particles is then placed in a flotation column or horizontal pipeline wherein the concentrated mineral is separated from the tailings containing the gangue. To be effective on a given ore slurry, the collectors are chosen based upon their selective wetting of the types of particles to be separated. A good collector will adsorb, physically or chemically, with one of the types of particles. In a flotation circuit for mineral concentration, various flotation reagents are added to a mixture of ore and water (called pulp) in a conditioning tank. The flow rate and tank size are designed to give the minerals enough time to be activated. The conditioner pulp is fed to a bank of rougher cells which remove most of the desired minerals as a concentrate. The rougher pulp passes to a bank of scavenger cells where additional reagents may be added. The scavenger cell froth is usually returned to the rougher cells for additional treatment, but in some cases may be sent to special cleaner cells. The scavenger pulp is usually barren enough to be discarded as tails. More complex flotation circuits have several sets of cleaner and re-cleaner cells, and intermediate re-grinding of pulp or concentrate. A typical slurry processing system is depicted in FIG. 1. As shown in FIG. 1, pulp slurry 8 is processed through a plurality of flotation cells 10 and the tailings 12 are discarded in a tailings pond or dam 100. If the processed slurry 9 can be further processed for mineral recovery, another flotation cell 10 may be used to repeat the process. When the processed slurry 9 is processed in the last flotation cell 10, froth flotation is generally no longer an effective or viable process for mineral collection. Because of a number of other factors, as much as 15% of the liberated minerals are not recovered and are discarded as gangue in the pond or dam 100.
There is a need in the industry to provide a better way to separate valuable material from unwanted material, from the discarded tailings.